For science images (which is what I work for) there is no real use in capturing things higher than 8-bit. I'm assuming that you're looking at either confocal stacks or stills from a light/fluorescent scope. For most things the fluorescent dye you're using has a pretty limited dynamic range, which means that your files are essentially bigger than they have to be.
While there is no "lossless" way to convert 16bit files to 8-bit files, in your place I would just use PS or Image J and simply save the files as 8-bit. I promise you that you will not notice a difference.
8-bit does not cut it for my scientific imaging. We do maximum intensity projections of 60-100 slice Z-stack confocal or widefiled images, followed by 3D blind deconvolution, followed by image analysis. We typically are looking for radiation or drug-induced nuclear foci, which we count as a measure of DNA repair capacity.
In this respect, 16-bit is absolutely necessary for working with the final images for quantification. First off, thresholding would be a nightmare with only 256 levels (vs. 65000+). Second, after deconvolving an 8-bit image, you can definitely see blocky pixels where the lack of gradiation between levels of grey is evident. You don't want to show this type of thing at a scientific meeting.
8-bit is fine for a lab meeting Powerpoint slide, but it doesn't cut it for quantitative analysis or for publication-quality figures. Remember, bit depth has nothing to do with dynamic range. You could have a 4-bit image with a 20 stop dynamic range (which would look blocky as hell), or a 16-bit image with a 2 stop dynamic range (which would look smooth). Bit depth is ALL about the gradiations between levels of grey.
